Temperatures in the low-to-high 30s across the region are causing the varied — and possibly dangerous — mix of precipitation. "Northern parts are seeing snow, central parts are sleet, and southern parts are seeing sleet and freezing rain," said Alan Dunham of the National Weather Service.

Dunham said that even parts of that state where it's raining, not snowing or sleeting, could have dangerous roads on Wednesday. "Where it's rain, the road drains are blocked up with snow so there's going to be a lot of standing water on the road," Dunham said.

Luisa Paiewonsky, the highway commissioner for the state's Department of Transportation, said no major accidents had been reported by midday.

Still, she warned that a predicted temperature drop Wednesday afternoon could make roads icy. "It'll change over to snow and freezing rain during the afternoon commute," Paiewonsky said. "There's potential for some flash-freezing."

Winter Storm Info

Wednesday's wet weather is also adding weight to existing snow, increasing fears of roof collapses. Peter Judge, of the Massachusetts Emergency Management Agency reported two minor collapses on Wednesday morning -- one in Springfield, and one in Northborough. No one was injured.

He said MEMA is concerned about more collapses later in the day, as the weather continues to change. "All of the snow that’s up there is going to turn into a giant sponge and absorb the rate of this rain," Judge said.

Judge said a FEMA search-and-rescue team is standing by.

Hundreds of schools had closed for the day, including Boston and Worcester public schools. That makes Wednesday the fifth snow day for the Boston Public School system.

More than a dozen lines were canceled on the commuter rail Wednesday morning -- a move by the consortium that runs it to reduce congestion and free up equipment and resources in case there were problems with the running trains. Services affected include six trains between North Station and Anderson Woburn on the Lowell line as well as four between North Station and Beverly, on the Newburyport/Rockport line.

The MBTA reported red line and bus delays. "Equipment, vehicles, and infrastructure have been battered by weeks of record snowfall and frigid temperatures. These conditions take a toll," said MBTA spokesman Joe Pesaturo.

The storm is part of a massive system that's brought blizzard conditions to parts of the Midwest, and could affect a full third of the U.S. population.